1. Field of the Invention
This invention relates to a method of manufacturing semiconductor integrated circuit interconnect structures. The invention relates more particularly to a method to alter heat flow on a localized basis when heating wafers to elevated temperatures to achieve different processing temperatures by altering the material properties, such as emissivity, absorptivity, and reflectivity, of a portion of a surface by the application of thin films of specified materials.
2. Background of the Invention
A. Field of the Invention
This invention relates to a method for fabricating semiconductor integrated circuit devices, specifically with a method for fabricating semiconductor integrated circuit devices enabling the creation of temperature differentials.
B. Description of the Related Art.
Semiconductor integrated circuit devices typically comprise silicon and multiple layers of vertically stacked metal interconnect layers with dielectric materials disposed between them. The fabrication of such devices typically involves the repeated deposition or growth, patterning, and etching of thin films of semiconductor, metal, and dielectric materials.
A substantial part of integrated device manufacture involves heating the wafers to elevated temperatures to promote a particular chemical reaction or to anneal the structure to achieve a desired metallurgical effect.
Typically, batch furnaces are used to heat silicon-based semiconductors during thermal fabrication steps. The furnaces heat primarily by radiation such that the wafers are in thermal equilibrium with the furnace surroundings. For example, as shown in FIG. 1, a batch furnace 10 may include a quartz tube 1 inserted into the core 2 of a furnace 3 that is heated resistively, where gas flows through the tube 1. Wafers 4 are placed inside the tube 1 and pushed into the core 2, where a uniform temperature is maintained. The heating elements 5 heat the core 2 and the wafers 4 with long-wavelength thermal radiation. Many wafers may be processed simultaneously and the cost of operation is divided among the number of wafers in the batch. A problem with using a furnace is that the wafers are susceptible to contamination from the hot processing in the core 2 on which deposited films may accumulate and flake off or through which impurities may diffuse and contaminate wafers 4.
Microprocessing environments for single wafers are now being used since control of contamination, process parameters, and reduced manufacturing costs are desired. In particular, rapid thermal processing (RTP) using transient lamp heating allows thermal processing to occur in a closed microenvironment. A rapid thermal processor 20 is shown in FIG. 2. A single wafer 11 is heated quickly under atmospheric conditions or at low pressure. The processing chamber 12 is either made of quartz, silicon carbide, stainless steel, or aluminum and has quartz windows 13 through which the optical radiation passes to illuminate the wafer 11. The wafer 11 is held, usually on thin quartz pins 18, in thermal isolation inside chamber 12. An ambient atmosphere inside chamber 12 is controlled by gas flow through chamber 12. Gas flows into the chamber 12 at gas inlet 14. Lamps 15 heat the wafer 11 through windows 13, aided by reflectors 17 above the lamps 15. A measurement system is placed in a control loop to set wafer temperature. Typically, an optical pyrometer 16 determines the temperature from radiated infrared energy on the back ofthe wafer 11, but thermocouples can also be used. The RTP system is interfaced with a gas-handling system and a computer that controls system operation.
The transfer of heat between objects is a function of their emissivity and absorptivity. For example, a perfect radiator or absorber has an emissivity of 1.0, whereas metals have much lower values around 0.1. Heat flow and emissivity are related by the following equation: EQU Q=.epsilon..sigma.T.sup.4
where Q is total heat flow in W/m.sup.2, .epsilon. is emissivity, .sigma. is the Stefan Boltzmann radiation constant of 5.67.times.10.sup.-8 W/m.sup.2.degree. K.sup.4, and T is the temperature in .degree. K.
In many cases, there are competing reactions occurring and it is desirable for these reactions to occur at different temperatures. Thus, to the extent the emissivity of a surface can be altered on a localized basis, a temperature differential can be achieved.
A method is known to apply a thin film on a surface to control reflectivity and emissivity. This film is applied to a wafer in a rapid thermal processor to alter the energy exchange. This method does not address selective application of film on the wafer to alter the temperature.
Another method is known for applying a film onto a substrate of a semiconductor, heating the substrate, and removing the layer. This method is used for reducing the effects of semiconductor deformities and does not address temperature differences in heating the wafer.
As a result, it is desirable to have a method that alters emissivity of selected portions of a surface to achieve a temperature differential.